You can use an assortment of lenses made to fit on F-mount. Sigma, Tamron, Tokina, Vivitar, Voiglander and not forgetting Carl Zeiss has lenses that can fit on Nikon F-mount.
It's pretty much the same for other makes like Pentax and Sony (Minolta) which also have their proprietary mount. An exception is Canon EOS because of the large diameter design, there are third party adapters to fit other lenses on the EF mount but these are not endorsed by Canon.
Do you intend to buy up the whole range of lenses? Even the often maligned small collection of Sony/Minolta's lens line up is sufficient to cover most if not all required situations, so why be bothered by this, afterall there are 3rd party lenses in the market. If the Nikon range of lenses still cannot satisfy you, i'm not sure which other system can.
All Nikkor lenses can mount on a Nikon body.
Can meter or autofocus or not is another story. :think:
All Nikon mount lenses made by Sigma, Tamron, Tokina, etc. can mount on a Nikon body too.
Nikon made a wide range of lenses for various usage. The only limit I find out is my wallet. :bsmilie:
All good and fast lenses are not cheap. Of course, there are some exception.
Of course, the price will be higher because of the monopoly. It is marketing, but you don't see Nikon or Canon complaining about the uniqueness of their lenses. That's why got 3rd party brands that makes lens to fit the nikon and canon bodies. Why would you think Minolta or the others are trying to have a common systems, while Nikon, Canon do not want to do so? Yet, Nikon & Canon have the major share of the market.
Erh...since when the other Brands are trying to have a common system? Minolta/Sony is using Alpha mount, Olympus is using 4/3 Mount and Pentax is using K mount. I only know that the common system in the past was the M42. :think: